Stale `OrderBookDB` entries remain in memory after `AMMDelete`

[mvadari]

Issue Description

In AMMCreate::doApply (src/libxrpl/tx/transactors/dex/AMMCreate.cpp, lines ~280–287), order books are added to the in-memory OrderBookDB:

ctx_.registry.getOrderBookDB().addOrderBook(book);

However, AMMDelete never removes these entries from the OrderBookDB. The in-memory DB is rebuilt from the ledger on node restart, so the stale entries are transient and self-healing. However, between deletion and restart, the stale entries may trigger unnecessary subscription notifications for empty book sides.

Steps to Reproduce

1. Create an AMM (which adds entries to OrderBookDB).
2. Delete the AMM via AMMDelete.
3. Observe that the OrderBookDB still contains the AMM's order book entries until the next server restart.

Expected Result

AMMDelete should remove the corresponding order book entries from OrderBookDB when deleting an AMM, similar to how AMMCreate adds them.

Actual Result

Stale order book entries persist in OrderBookDB until the server restarts and rebuilds the DB from the ledger.

Environment

All versions with AMM support (XLS-30).

Supporting Files

N/A